In the vehicle construction as well as in the aircraft industry, fastening elements are used e.g. for coverings, which must fulfill specific requirements. To avoid machining steps in response to the final assembly, plate-shaped elements are pre-drilled, e.g., and are provided with clips or inserts, respectively, which have further screwing elements, which are elastic or which are attached with play, prior to the final assembly. In response to the final assembly, the connectors or fasteners, respectively, to other covering elements or structurally bearing elements, respectively, then engage with these screwing elements or snap retainers, respectively. The plate-shaped elements or components, respectively, are hereby frequently lightweight construction elements or sandwich panels, respectively, which, for weight reasons, predominately consist of two outer layers (of plastic or aluminum), which are adhered with a honeycombed reinforcement therebetween.
A clip 10 of the mentioned type is shown in FIG. 1. On principle, it has the basic shape of a clamp comprising a first leg 11 and a second leg 12 comprising a connecting web 13. For the assembly, the clip is pushed onto a plate (only suggested, 18), so that a fastening element 20 comes to rest above a prepared opening in the plate (covered in FIG. 1). This fastening element 20 substantially consists of a plate-shaped base (not visible in FIG. 1) comprising two lugs (protrusions 14, 15) and a nut part 21. The two protrusions 14, 15 are in each case held in a frame or by a bracket 16, 17, respectively, which spans the lugs, of the side plates 19, 22 of the upper clip leg 11. The frames are embodied in such a way that the fastening element 20 has lateral play, but cannot fall out of the clip. The fastening type, which the fastening element 20 allows, can be realized in many alternatives, for example as releasable or non-releasable snap-in connection comprising a fixed or a plurality of catches. The cylindrical section 21 can furthermore have an internal thread for a screw. A screw connection hereby has the advantage of being releasable and the possibility of tightening torque control.
Depending on the application profile, the fastening element 20 can be made of metal or plastic. If high strengths are required, metal is preferred, but represents a challenge in response to the production. Very high production costs are to be expected for turned/milled parts. A fastening element can thus also be made of wire, tape material or sheet metal in a multi-stage forming process, but thereby also runs through a plurality of operation cycles and must subsequently possibly be subjected to a heat treatment.
In response to the use of a lightweight construction fastener, in response to its assembly, a fastener is guided—in FIG. 1 from below—through a recess in the leg 12, an opening which is brought into alignment in the plate 18, and a further opening in the upper leg 11, and is connected to the fastening element 20 at that location. The plate 18 is thus fastened to a different element. There are many variations of this type of clip fasteners with different leg lengths, shapes and for different plate thicknesses.
U.S. Pat. No. 4,219,064 shows the basic principle of such a fastener made of metal, the more recent U.S. Pat. No. 6,474,917 shows an embodiment with plastic clip and a fastening element of metal. Both publications focus on an arrangement, in the case of which openings are provided in the side plates on the longitudinal side of the clip. In the case of U.S. Pat. No. 4,219,064, this arrangement results due to the production of a plate-shaped sheet metal part, out of which the openings are punched out on the side and two tabs comprising those very openings are subsequently bent by 90° to form side plates. This results in a structural reinforcement of the upper leg. The later U.S. Pat. No. 6,474,917 adopts the arrangement and forms the side plates of plastic with the corresponding openings.
This arrangement, however, also has disadvantages: Due to the arrangement of the fastening element 20 at right angles to the longitudinal extension of the upper clip leg, the fastening element or the embodiment of the protrusions 14, 15, respectively, defines the width of the clip. The frames 16, 17 must additionally be designed in such a way that they can also fulfill the described reinforcing effect, even though the holding openings are at a structurally unfavorable location in the side wall, namely exactly at the height of the clip, at which the force introduction occurs by the fastening element. Due to the fact that the fastening element and the clip are typically made and assembled separately (by snapping in after briefly pushing away one of the frames), a stable frame has a negative impact on the ease of assembly of the fastener: the more stable the frame, the more stable the lightweight construction fastener per se—but the more difficult the production.